The goal of this R01 proposal is to identify genetic variants that affect complications and risks of allogeneic hematopoietic cell transplant (HCT). Validated discoveries will provide the information necessary to greatly improve risk assessment, counseling, treatment planning and to direct future mechanistic studies of the genes and pathways that control the complex post-HCT phenotypes thereby providing insight and rationale for new targeted therapies. The immediate objectives of this proposal are (1) to enlarge the existing discovery cohort to significantly increase power for detecting additional genetic variants associated with HCT outcomes; (2) perform an in silico candidate gene study using the GWAS-HCT database to replicate results of previously published studies; and (3) develop an innovative approach to i) measuring genome-wide genetic disparity between donor and recipient, and using this measure to test for association with GVHD, relapse and mortality, and ii) identifying non-MHC loci encoding minor histocompatibility antigens that serve as the targets for GVHD and the graft-vs-leukemia (GVL) effect. The current research effort will represent an extension of a GWAS-HCT we initiated in 2006 with the support of R01 HL087690 (09/25/2006-07/31/2009) which generated genome scans for 1,553 HCT cases (>3,000 patient and donor samples) using the Affymetrix 5.0 GeneChip. Analyses thus far have revealed associations with loci conferring risks of 2-fold or greater. However, effects below this threshold, which may identify many more novel pathogenic pathways, require greater statistical power. The first specific aim is to expand the GWAS-HCT project to include all patients transplanted at our Center from 1988 through 2009, bringing the total number to ~5,000 transplants (~10,000 patients and donors). Increasing the sample size by >300% will improve power for detecting genetic variants associated with HCT outcomes across a range of odds as low as 1.5, and provide opportunity for including additional high priority but low incidence clinical phenotypes that occur in this patient population with a frequencies as low as 10-15%. The HCT outcomes phenotypes analyzed will include acute and chronic GVHD, immunological tolerance, airflow obstruction (AFO disease/bronchiolitis obliterans syndrome (BOS), acute kidney injury (AKI), Gram negative bacteremia, invasive fungal disease, CMV infection and disease, disease relapse and transplant-related mortality. We will also apply an innovative approach to the analysis of recipient-donor genetic disparity to identify the minor histocompatibility genes responsible for GVHD and the graft-vs-leukemia (GVL) effect. This comprehensive genetic and rich phenotype data will be available through dbGaP, and will provide a novel opportunity for leveraging HCT genetics for the broader improvement of HCT safety and efficacy.